N‑Doped\nCarbon-Incorporated\nCobalt–Iron\nMixed-Metal Phosphide Nanoboxes as Efficient Bifunctional Catalysts\nfor Overall Water Splitting

Optimizing the composition and structure\nof nanocatalysts\nis an\nefficient approach to achieving the top electrocatalytic performance.\nHowever, the construction of hollow nanocomposites composed of metal\nphosphides and highly conductive carbon to promote the electrocatalytic\nperformance of metal phosphide-based catalysts is rarely reported.\nHerein, a CoFeP/C nanobox nanocomposite consisting of Co–Fe\nmixed-metal phosphides and N-doped carbon was successfully fabricated\nthrough an ion-exchange phosphidation strategy derived from ZIF-67\nnanocubes. Benefiting from the synergistic effects between multiple\ncomponents and the unique hollow structure, CoFeP/C nanoboxes can\ncatalyze the alkaline oxygen evolution reaction (OER) and hydrogen\nevolution reaction (HER) with high activity and stability. Furthermore,\nin the construction of an alkaline water electrolyzer using CoFeP/C\nnanoboxes as both OER and HER catalysts, they were capable of efficiently\nsplitting water with a current density of 10 mA cm<sup>–2</sup> achieved by applying only 1.62 V of cell voltage and exhibited outstanding\ndurability. Density functional theory calculations demonstrate that\nsynergistic effects among multiple components in CoFeP/C nanoboxes\ncan lower the hydrogen adsorption free energy of the HER and OER energy\nbarrier of the rate-determining step, thus promoting the catalytic\nreactions. The design and synthesis of CoFeP/C nanoboxes highlight\nthe importance of the composition and structural characteristics in\nachieving high-performance water electrolysis.